Technical Field
This application relates generally to solar collectors, and more particularly to optimization of geometric fill factor in a solar collector that is fed via prism-coupled optical waveguide(s).
Background Information
A Monolithic Thin Film Concentrating (MTFC) Solar Collector with an option for Spatially Separated Photovoltaic (PV) Devices has the potential to provide improved efficiency, while lowering the manufacturing cost over conventional solar concentrating systems. The monolithic structure is divided into three (3) major areas: 1) a uniform leaky-wave solar antenna, 2) a waveguide and 3) a PV device region. Here, the PV can be any combination of photovoltaic optical to electrical converting device such as a semiconductor or an antenna-coupled metal insulator metal (MIM) device(s). This entire structure lends itself to fabrication using thin film processes typical in the semiconductor industry that produce Complementary Metal Oxide Semiconductor (CMOS) circuits. Processes such as Metal Oxide Vapor Chemical Deposition (MOVCD), Plasma-Enhanced Chemical Vapor Deposition (PECVD) and Reactive Ion Etching (RIE) are well suited to cost-leverage by high volume production.
More details of such a device are provided in a co-pending U.S. patent application Ser. No. 13/357,448 entitled “Leaky Wave Mode Solar Receiver” filed Jan. 24, 2012, the entire contents of which are herein incorporated by reference.
The discriminating features of this solar cell design come from the application of electromagnetic theory, similar to phased array antennas, to the light propagation. The sun's energy is concentrated using a wide-band uniform leaky-wave solar “antenna” that couples the energy into a planar waveguide. Optical coating filters within the waveguide, direct the spectral energy bands into photovoltaic devices, each having a band-gap optimized to the wavelength of energy incident on each of them. The unique features of this arrangement are; the uniform leaky-wave antenna region is broadband, collecting the entire solar spectrum. The capture area of the antenna has a wide field of view in one (1) plane which eliminates the need for 2-axis tracking. Tracking in the single axis is accomplished by electro-mechanical means with the use of MEMS actuators to physically tilt the sub-arrays, conventional solar trackers, or by controlling the propagation constant in the traveling wave array structure with piezoelectric actuators which adjust the phase progression on the antenna and allows for beam steering without physically tilting the array.
The waveguide structure is designed to be optimized for the solar spectrum and coherently directs energy to the photovoltaic region. One aspect to lowering the cost is in using multiple, spatially separated photovoltaic devices. By separating the devices, the costs, design constraints and inefficiencies associated with lattice matching and tunnel diode junctions are eliminated. Furthermore, this structure takes advantage of the strengths of Concentrated PV (CPV) approaches, such as higher efficiencies of PV devices under concentration, and the reduction of PV material, while reducing the major costs involved in CPV systems such as the high cost of optics, trackers, and tandem multi-junction PV cells. By applying a systems engineering approach, all the key components are integrated into the monolithic architecture to yield a system that reduces the cost of generating solar power through an increase in efficiency while lowering manufacturing costs.